Instead, include a few powerful ones that work well with incidental graveyard growth and enjoy the extra value, as, in general, chasing threshold wont be worth the effort
Maddening Cacophony doesnt really fit the theme of the rest of the Secret Lair, but its on brand for the reaction this drop might cause
Legendary creatures you control gain protection from each of that creatures colors until end of turn

Abaddon the Despoiler Abdel Adrian, Gorion's Ward Absolute Virtue Abzan Guide Abzan Kin-Guard Academy Raider Accursed Marauder Adder-Staff Boggart Agent Frank Horrigan Ahn-Crop Champion Ahn-Crop Crasher Ahn-Crop Invader Ainok Strike Leader Ajani, Nacatl Pariah Akiri, Fearless Voyager Akki Avalanchers Akki Ember-Keeper Akki Lavarunner Akki Raider Akki Underling Akoum Boulderfoot Akoum Warrior Akroan Line Breaker Al Bhed Salvagers Alesha's Vanguard Alesha, Who Laughs at Fate Alesha, Who Smiles at Death Allosaurus Rider Alpine Houndmaster Ambassador Oak Anep, Vizier of Hazoret Angel of Indemnity Anthousa, Setessan Hero Arashin Foremost Arashin Sunshield Archetype of Aggression Arctic Nishoba Ardbert, Warrior of Darkness Ares, God of War Armored Skaab Armory Veteran Ash Zealot Ashenmoor Cohort Ashenmoor Gouger Aspiring Champion Assault Intercessor Astelli Reclaimer Astor, Bearer of Blades Atarka Beastbreaker Atarka Pummeler Attuma, Atlantean Warlord Aurora Champion Avalanche Tusker Aven Eternal Aven Gagglemaster Aven Initiate Aven Reedstalker Aven Skirmisher Aven Sunstriker Aven Wind Guide Avenger of the Fallen Avenging Huntbonder Axegrinder Giant Axgard Braggart Azra Bladeseeker Azra Oddsmaker Backwoods Survivalists Baldin, Century Herdmaster Ballroom Brawlers Banewhip Punisher Barktooth Warbeard Barkweave Crusher

It works, but it looks and feels like 2012